The present invention relates to a semiconductor device for switching, such as a thyristor, and a manufacturing method therefor.
A planar thyristor or the like is known as a typical semiconductor device for switching. A planar thyristor is superior to a mesa thyristor in terms of reliability, yield, ease of handling, and the like. However, a planar thyristor has a smaller electrical capacity (e.g., a withstand voltage and a maximum switching current) than a mesa thyristor. This drawback is due to poor yield when a planar thyristor of a large capacity, having an enlarged area for a switching element pellet is manufactured by a conventional technique. However, as current wafers now have larger diameters, a planar thyristor having a high withstand voltage, and high reliability has consequently become desirable. Among these characteristics, a high withstand voltage can be realized by moderating the rise of the surface electric field on a p-n junction, by means of a field plate structure. In this case, the increase in pellet size is negligible. However, in order to enhance the reliability of such a thyristor, erroneous firing at high temperature must be prevented, and a suitable resistance must be provided between the gate and cathode of the thyristor. Such a resistance also serves to provide a constant fire sensitivity of the thyristor. This resistance can be formed by means of a diffusion resistor or polysilicon resistor. However, in either case, the pellet size is enlarged, as a whole, if the resistance is added to a conventional thyristor structure.